Werk #14424: Interface services: Do not abort upon counter overflow

Most of the interface check plugins (such as if64) are counter-based. This means that the rates shown in the service outputs are computed by Checkmk based on these counters. One property of these counters is that they may overflow and subsequently re-start from zero. When this happens, no useful rate can be computed for this check cycle.

Before this werk, Checkmk aborted and did not produce any service output in this case. Now, Checkmk instead skips the metrics for which the corresponding counters overflowed, but still produces the remaining, unaffected results.

Note thas this only applies to ungrouped interfaces, i.e. the vast majority of all interface services.

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